NAND flash memory, as well as other types of non-volatile memory (“NVM”), is commonly used in electronic devices for mass storage. For example, consumer electronics such as portable media players often include flash memory to store music, videos, and other media.
Non-volatile memory devices, however, may develop defective memory cells through normal, everyday use, and operational memory cells may suffer from program/erase/read disturb due to voltages applied to the cell being addressed or neighboring cells. When a memory location, such as a page, of a NVM contains too many defective cells or otherwise becomes unusable from excessive errors, the information contained within that memory location may be lost. When this occurs, the electronic device using the NVM might lose user data (e.g., data stored by an application). In addition, the electronic device might lose metadata that the electronic device uses to manage the NVM. This can have a negative affect on the performance of the non-volatile memory.
In some circumstances, there have been attempts at protecting the metadata by storing redundant copies of it in a location other than where the user data is stored. For example, U.S. patent application Ser. No. 12/562,860, which is incorporated by reference herein in its entirety, describes systems and methods for utilizing redundantly stored metadata in which all of the redundant metadata would be stored in a similar manner, such as the “left-of-me” method. While those attempts may have had some measure of success, they become less reliable and more prone to error when the user data in question is located close to periphery of the organizational structure of the memory device. For example, if the user data is stored close to or at the end of a superblock, or such that it crosses a superblock boundary, there is a strong likelihood that the redundant metadata will be lost (e.g., they may not be a cell to the right of the one in which the user data is stored).